Malignant hyperthermia (MH) was observed in three cases of Halothane anesthesia performed in six littermate pigs. In two pigs, MH was totally reversed by the intravenous administration of Dantrolene 2 or 3 mg/kg. In one pig, an injection of 2 mg/kg reversed the MH symptoms transiently Dantrolene had no effect on the serum lactate values elevated in the MH-positive pigs. The therapeutic use of Dantrolene appears to be indicated in the stress-susceptible pigs.